This invention relates to a mask and a device manufacturing method using the same, for use in the production of various devices such as semiconductor chips (e.g., ICs or LSIs), display devices (e.g., liquid crystal panels), detecting devices (e.g., magnetic heads), or image pickup devices (e.g., CCDs), for example.
Due to increases in density and speed of a semiconductor integrated circuit, the linewidth of a pattern of an integrated circuit has been narrowed and further improvements in performance of semiconductor manufacturing methods have been required. In order to meet such requirements, in the field of exposure apparatuses for forming a resist pattern in a lithography process, among semiconductor manufacturing processes, steppers which use shorter exposure wavelengths such as extreme ultraviolet light (e.g., KrF laser (248 nm), ArF laser (193 nm) or F2 laser (157 nm)) or X-rays (0.2-15 nm), for example, have been developed.
In an exposure process using extreme ultraviolet light, usually reduction exposure of 4:1 to 5:1 is performed. Therefore, a reticle (original) is formed with a pattern of a size which is 4xc3x97 to 5xc3x97 larger than a pattern to be produced on a wafer. In an X-ray proximity exposure process which is a unit magnification process, on the other hand, an X-ray mask (original) should have a very fine pattern of the same size as a pattern to be produced. For this reason, the X-ray mask manufacture is one of the key technologies in the X-ray proximity exposure.
Referring to FIGS. 10A-10F, a conventional X-ray mask manufacturing method will be described.
As shown in FIG. 10A, a supporting frame 1 is provided by a Si substrate, on which an X-ray transmissive film 2 made from a SiC film is formed. As shown in FIG. 10B, an X-ray transmission region is defined, by etching the supporting frame 1. Thereafter, an X-ray absorptive material 3 is provided by a film of W, whereby a structure shown in FIG. 10C is produced. The film formation may be made before the etching process in FIG. 10B.
Subsequently, an electron-beam resist 4 is applied to the substrate, whereby a structure shown in FIG. 10D is obtained. Because of X-ray exposure of unit magnification, data is prepared to draw a pattern exactly the same as a pattern to be produced on a wafer (workpiece). Then, while using an electron-beam exposure apparatus, the electron-beam resist is patterned. Through a subsequent development process, a resist pattern such as shown in FIG. 10E is produced. Then, as shown in FIG. 10F, a dry etching process is performed, whereby a desired pattern of X-ray absorptive material is produced. The X-ray transmitting region (not shown) may be formed after the formation of the X-ray absorptive material pattern. With the procedure described above, an X-ray mask having an X-ray absorptive material of desired shape is produced.
In the conventional X-ray mask manufacturing procedure such as described above, there are limits in resolution and positional precision, for the following reasons.
As regards electron-beam pattern drawing apparatuses used for the manufacture of originals, the position of electron beam irradiation is controlled by applying an electromagnetic or electrostatic field to an electron beam to deflect the same. Thus, the controllability of an electric voltage to be applied to a deflector is critical to the position control for a pattern. Usually, in order to draw a very fine pattern, the drawing is performed while the beam is restricted narrow. Therefore, the voltage level is low, while the data is huge. Both the data transfer time and the patterning time are very long, and finally it takes an extraordinarily long time (more than a few hours) to finish the patterning for an X-ray mask. This causes a possibility of drift during the patterning process. Particularly, in the case of a chemical amplification type resist which has recently been developed for resolution of a very narrow linewidth, the oxide diffusion distance may vary during a time period from exposure to baking, which is critical to the linewidth and shape of the resist. It is, therefore, not easy to use these types of resist materials in the patterning exposure process, which requires a very long time.
As described above, in accordance with current mask manufacturing procedures using electron beam patterning technologies, the electron beam has to be narrowed to increase the resolution, but it causes considerable prolongation of the patterning time, on one hand, and undesirable degradation of positional precision, on the other hand. Further, the required electron-beam patterning time adversely affects the throughput and cost of the X-ray mask production.
U.S. Pat. No. 5,623,529 proposes a method of reproducing an X-ray mask on the basis of X-ray exposure, in an attempt to increase the throughput and reduce the cost. Since, however, an original itself for X-ray masks has to be produced using electron-beam drawing, there still remain inconveniences although the resolution and positional precision may be improved.
It is an object of the present invention to provide a mask manufacturing method by which a high precision mask can be produced.
It is another object of the present invention to provide an X-ray mask manufacturing method by which an X-ray mask having a very high precision, higher than one attainable with current technologies, can be produced with use of a current electron-beam patterning apparatus and exposure apparatus, with a result of improved throughput and reduced cost.
It is a further object of the present invention to provide a high precision X-ray mask such as described above.
It is a yet further object of the present invention to provide an X-ray exposure method, an X-ray exposure apparatus, a semiconductor device, and a semiconductor device manufacturing method, using such an X-ray mask.
In accordance with an aspect of the present invention, there is provided a mask manufacturing method, comprising the steps of: performing a multiple exposure process to a substrate so that a number of latent images are formed on the substrate; and processing the exposed substrate to produce actual mask patterns.
The multiple exposure process may include (i) a first exposure step for forming a latent image of relatively-fine periodic patterns on the substrate by use of a first master mask having absorptive periodic patterns, and (ii) a second exposure step for forming a latent image of relatively-rough patterns on the substrate by use of a second master mask having absorptive patterns.
The first exposure step may include transferring a pattern of the first mask onto the substrate with a magnification 1/N where N is an integer not less than 2.
The first exposure step may include adjusting a gap between the first mask and the substrate.
The processing step may include a developing step and an etching step.
The first mask may be prepared by use of a first electron beam, and the second mask may be prepared by use of a second electron beam having an address size and a beam diameter, at least one of which may be different from that of the first electron beam.
In accordance with another aspect of the present invention, there is provided a mask manufacturing method, comprising the steps of: preparing a first mask through a procedure including (i) a first exposure step for forming a latent image of relatively-fine periodic patterns on a substrate by use of a first master mask having absorptive periodic patterns, and (ii) a second exposure step for forming a latent image of relatively-rough patterns on the substrate by use of a second master mask having absorptive patterns; and preparing a second mask through a procedure including (iii) a third exposure step for forming a latent image of relatively-fine periodic patterns on a substrate by use of a third master mask having absorptive periodic patterns, and (iv) a fourth exposure step for forming a latent image of relatively-rough patterns on the substrate by use of a fourth master mask having absorptive patterns; wherein the third master mask is the same as the first master mask.
The method described above may be used to produce a mask to be used for X-ray lithography.
The mask to be produced may comprise a structure having a membrane on which the actual mask patterns are formed, and a frame for supporting the membrane.
In accordance with a further aspect of the present invention, there is provided a semiconductor device manufacturing method, comprising the steps of: preparing a mask by performing a multiple exposure process to a substrate so that a number of latent images are formed on the substrate, and by processing the exposed substrate to produce actual mask patterns; and using the prepared mask in an exposure process so that the actual mask patterns are transferred to a wafer, for manufacture of semiconductor devices.
The exposure process may use X-rays.
In accordance with a yet further aspect of the present invention, there is provided an exposure apparatus for transferring a mask pattern onto a substrate, by use of a mask prepared in accordance with a method such as described above.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.